Thermographic reproduction paper and method of using



Dec. 15; 1964 G. c. HUETT ETAL 3,161,770

THERMOGRAPHIC REPRODUCTION PAPER AND METHOD OF USING Filed March 20,1962 FIG. I

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' REDUCING CARBOHYDRATE flfAC/D 3 2 GEORGE C. HUETT HZERTWELLGL.

BY 44 W ATT'YS United States Patent 3,161,770 THERMOGRAPHIC REPRODUCTIONPAPER AND METHOD OF USING George C. Huett and Hartwell L. Briggs,Chicago, and Ken G. Prohst, Northlake, Ill., assignors to EugeneDietzgen Co., Chicago, 11]., a corporation of Delaware Filed Mar. 20,1962, Ser. No. 181,091 4 Claims. ((Il. 250-65) The subject inventionrelates to the production of thermographic paper. More particularly, thepresent invention is directed to improved copying materials which arecapable of producing a facsimile copy by means of radiant energy.

In the past several years, various types of copy paper have beendeveloped which produce a facsimile copy when exposed to radiant energysuch as infrared light beneath graphic subject matter set forth on anoriginal. A typical thermographic process is described in the patent toMiller, U.S. 2,740,896. As is disclosed in this patent, carbon inks andcertain other marking means absorb radiant energy from infrared bulbscreating heat. This energy is transferred to a sensitized sheet of copypaper in contact with the original causing the formation of duplicatecharacters.

A wide variety of materials have been used as color producing bodies incoating the copy paper. In heat developable diazotype reproductionsystems, for example, the copy paper is coated with a diazo compound, aconpler, and a compound which produces an alkaline reaction when heated.In other systems such materials as nickel acetate, silver nitrate,sodium behenate, ferric stearate, etc., have been used as components ofthe color producing coating.

It has been found that compositions of the above type often havedisadvantages, especiallywhere the copy paper is to be used on acommercial basis. Such materials, for example, often tend to be unstableboth prior to development and subsequent to. the formation of thefacsimile, which facsimiles cannot be used asintermediates for producingother copies of the original. Additionally, many of the known coatingcompositions are relatively expensive and are diflicult to handle on acommercial scale. a t

It is an object of the present invention to provide improved copy paperfor thermographic reproduction systems.

Another object of the invention is to provide thermographic paper whichcan be produced inexpensively and without difficulty.

Still another object of the invention is to provide copy paper whichwill produce accurate and clear facsimiles.

Still another object is to provide copy paper which can producefacsimiles of original which are printed on both sides.

Another object is to provide copy material which can be used to produceread-out copies or intermediates regardless of whether the copy materialis coated on one side or both sides.

Another object is to provide copy paper which in addition to blackcharacters will reproduce characters of certain other colors to areadable degree.

Still another object is to provide copy paper which can be used toproduce facsimiles having well defined char- "ice acters and withoutcausing the blurring of surrounding background areas.

Other objects will become apparent to those skilled in the art from thefollowing detailed description of the invention.

In general, the invention comprises the discovery of a process by whicheither the cellulose in paper or carbohydrates coated on a suitable basecan be treated so that a color image will be produced by means ofradiant energy transferred from the characters of the original to thecopy sheet. If the cellulose of the paper is to be transformed into thecolor forming body, it is only necessary to coat the sheet with anaqueous solution containing particular amounts of particular acidspreferably along with certain stabilizing agents. In the secondembodiment of the invention paper or another base is coated with asolution of a carbohydrate such as lactose, glucose, mannose, etc.,along with particular amounts of particular acids, preferably againwith. certain stabilizing agents.

If the paper itself is to produce the color forming body, the coatingcomposition consists of an aqueous solution of an acid such asmeta-benzene disulfonic acid along with a stabilizing agent such asurea. When the paper is heated by the transfer of energy from thecharacters of the original to the copy sheet, the cellulose appears tobreak down forming a reducing type carbohydrate. The carbohydrate givesup water to form a cyclic aldehyde compound of the furan type such ashydroxymethyl furfural. Under the conditions prevailing during theheating step, the cyclic aldehyde polymerizes forming a brown character.The color of the character can be modified by adding co-reactingcomponents to the coating solution.

In the second embodiment of the invention, the carbohydrate contained inthe coating solution takes the place of the cellulose of the paper. Thecombined action of the acid and the heat converts the carbohydrate intoa cyclic aldehyde compound of the furan type such as hydroxymethylfurfural or furfural. This material polymerizes to form a coloredcharacter corresponding to the characters of the original.

The invention is illustrated in theattached schematic drawing in which:

FIGURE 1 is an enlarged fragmentary cross-section of a sheet ofreproduction paper embodying the invention and shown in print makingrelation to a cross-section of the original to be copied; and

FIGURE 2 is an enlarged fragmentary cross-section of a sheet ofreproduction material which illustrates a modified process which may bepracticed in carrying out the subject invention.

The reproduction or copy material 1 illustrated in the drawing iscomposed of a sensitive layer 2 on a base 3. In the first embodiment ofthe invention, the sensitive layer 2 consists of paper which has beentreated with a particular aqueous acid solution, preferably along with astabilizing agent such as urea. In the second embodiment of theinvention, the sensitive layer 2 contains a carbohydrate such asmannose, glucose, etc., a particular acid, and preferably a stabilizingagent. In the second embodiment of the inventiombase 3 can either bepaper or another material such as'clear plastic, glass cloth, etc. Thebase, of course, should be capable of transmitting radiant energy.

FIG. 1 illustrates a front printing process which constitutes apreferred embodiment of the invention. In

this process the sheet of reproduction material 1 containing sensitizedlayer 2 on base 3 is superimposed on master or original 4 forming anexposure sandwich S. The master consists of a sheet or base layer 5 ofpaper or graphically markable sheet material containing a design,drawing, written or typed character 6 to be copied. As is indicated inthe figure, character 6 can be on both sides of the sheet in the frontprinting system. Radiations Re such as visible light in the orange andred spectral zones as well as invisible infrared radiation is producedby radiation source 7. The radiations Re pass through the copy material1 and strike the face surface 8 of original 4. Radiation strikingcharacter 6 of master 4 are converted to heat which is conducted asindicated at H to the sensitive layer 2 of the reproduction material. Animage 6" is produced which duplicates original character 6. Radiationsthat are not absorbed either are reflected as shown at 9 or aretransmitted through the materials. Where the original is printed on bothsides, the unabsorbed radiations are reflected by adjusting radiationsRe. The radiations are focused on the surface of the copy paper in anelongated zone normal to the face of the sandwich, while the sandwichmoves with respect to said zone in the direction of the arrow. If it isdesired,,the base 3 can be coated or synthesized on both sides. Underthese circumstances, the print would appear both on the front and theback of the copy sheet.

In FIG. 2 a back printing method is described in which reproductionmaterial 1 is beneath master or original 4. Once again, the masterconsists of a sheet or base layer 5 of paper or graphically markablesheet material containing a design, drawing, written or typed character6 to be copied. The master is superimposed on the sheet of reproductionmaterial 1 to form an exposure sandwich S. Radiations Re such as visiblelight in the orange and red spectral zones as well as invisible infraredradiation is produced by radiation source 7. The radiant energy source 7preferably is arranged so as to scan the original and copy materials.Radiations Re are concentrated and focused on the face surface 8 of theoriginal in an elongated zone normal to the face of the drawing, whilethe sandwich moves with respect to said zone in the direction of thearrow. As each portion of the sandwich passes through the focal zone,radiations are absorbed by the design area 6 and are converted to heat,which, as shown at H, is conducted through the base 5 of the original 4,to the sensitive layer 2 of the copy material. In embodiment one of theinvention, this heat converts the cellulose or paper into a colorproducing polymer producing duplieating character 6". In embodiment twoof the invention, the heat converts the reducing carbohydrate into acolor producing polymer to produce duplicate character 6".

The radiations which are not absorbed by character 6 are re flected asis illustrated at 9, or they may be transmitted through base 5 of theoriginal depending upon the materials used. These rays normally donotafiect the face surface. 1

As was pointed out above, it is essential that the reproduction paper orcoated base be treated with particular solutions of particular organicacids. In embodiment one of the invention, the following organic acidshave been found to be satisfactory:

reproduction if the original contains a design only on its In' general,.organic acids, having dissociation constants varyiii'g from thatofcitr'ic acid to that of benzene .sul-

fonic acid are satisfactory. In other Words, the acid should not bestronger than benzene sulfonic acid nor weaker than citric acid.

The reducing carbohydrates which can be used in the second embodiment ofthe invention include monosac charides such as galactose, glucose,mannose, gulose, etc.; oligosaccharides such as maltose, lactose,cellobiose, etc.; polysaccharides, cellulose, starch, pentoses such asarabinose, ribose, xylose, and lyxose, etc., and ketose sugars such asfructose. These carbohydrates act in much the same manner as thecellulose of the paper when treated with the particular acid solutionand when heated by radiant energy in the manner described above once ithas been broken down to a saccharide. The carbohydrate forms cyclicaldehyde compounds which polymerize to form color bodies. Additionally,certain oxidation side reactions take place producing other color bodiessuch as humines.

The following examples are illustrative of the subject invention.

Example I In this example reproduction paper was treated with acomposition made up of the following ingredients:

Water -n 100.00 'mBDSA 28.50 Urea 14.40 Thiourea 0.50 CdSO 8H O 10.50

The solution Was applied to the paper with a solutionwet roller,although other suitable means could be employed such as spraying, kisscoating, slot fountain, etc. After the excess was removed the paper Wasdried for about two minutes in a drying oven held at 70 C. and wasplaced in sandwich relationship with a superimposed original containingtyped graphic characters. The sandwich was placed beneath an infraredbulb whereby radiation from the radiation source was absorbed by thegraphic characters on the original. Heat was transferred to the copypaper which caused a polymerization reaction to occur forming coloredareas which duplicated the characters of the original. The temperatureof the paper in the polymerization areas was about 360 F. An excellentreproduction of the original was obtained by this method. The charactersof the facsimile were brown in color.

In the preferred embodiment of the invention, the copy paper issuperimposed on the original, in which case a front printing system isused as is illustrated in FIG. 1 of the drawing.

3 Example llf In this illustrative experiment, cellulosic reproductionpaper was treated with the following solutions:

Meta- Bleached Water, g. benzene Urea, g. can

disulfonic sugar, g.

acid, g.

sults. In all of the above tests, the front printing system.

disclosed in FIG. 1 of the drawing can be used in place of the directenergy transfer method shown in FIG. 2 of the drawing.

It has been found that the subject process has little, if any,detrimental effect on the strength of the copy paper. In the firstembodiment of the invention, for example, the degradation of the papercellulose is relatively slight. The same is true of the coated papers ofthe second embodiment of the invention. As was pointed out above, theaddition of copolymerizable compounds to the aqueous acid treatingsolution produces varying colors. This fact, among others, makes itclear that in the first embodiment of the invention the combined actionof the acid and the heat does not produce charring of the paper.

The amount of acid used in both embodiments of the invention can varyfrom about 20 to about 35 grams per 100 grams of Water. If an organicsolvent such as ethyl alcohol, isopropanol, butanol, ethyl Cellosolve(or other low molecular weight alcohols) or benzene or toluene, etc., isused rather than water, the amount of acid can vary from about 2 toabout 35 grams per 100 grams of solvent. The amount of urea or otherstabilizing agent can vary from gram to about 20 grams, preferebly 2-l0grams, per 100 grams of Water. If it is desired, a metal sulfate such ascadmium sulfate, nickel sulfate, and cobalt sulfate can be added to thetreating solution as an additional stabilizing agent. The amount of themetal sulfate can vary from 0 to about 15 grams per 100 grams of water.

The amount of carbohydrate that is used in the coating solution can varywidely. It has been found that from about 0.5 gram to about 20 grams ofcarbohydrate per 100 grams of Water or organic solvent is satisfactoryin most instances. The preferred carbohydrate range is from about 2 toabout 10 grams per 100 grams of water.

In the second embodiment of the invention the coating solution isapplied to the base in an amount varying from 5 to 30 grams, preferably8 to 20 grams,per square meter. The drying time for the paper generallywill be from about 1 to about 3 minutes depending upon the temperatureof the drying oven. A suitable oven temperature would be between about60 C. and about 80 C.

As was indicated above, the temperature of the paper in the areas of thepolymerization reaction will Vary from about 240 F. to about 360 F. Thetemperature required to produce a satisfactory print, of course, willdepend upon the printing speed, the voltage across the lamp source, etc.In most instances, the paper need be exposed to the radiation for only abrief period of time, for example, from 0.05 second up to about 3seconds, and preferably from 0.1 to 0.5 second.

In carrying out the subject process, it is not necessary to use binderresins to hold the applied coatings to the surface of the base. If it isdesired, however, watersoluble or water-emulsifiable polymers can beused such as polyvinyl acetates, acrylic type polymers, polyvinylacetates-acrylic type copolymers, water-soluble alkyd resins,water-soluble polyesters, water-soluble alkyd-copolymers type, etc.

The degree of print strength depends upon (1) temperature, (2) time, and(3) the degree of polymerization which takes place. The degree ofpolymerization is determined by the type of organic acid that is used inthe sensitizing step and its concentration. Acids that are weaker thancitric acid do not produce distinctive prints, while inorganic acidswhich are oxidizing in nature often cause carbonization of thecarbohydrate. For these reasons only organic acids should be used havingan ionization constant varying from that of citric acid to that ofmeta-benzene disulfonic acid.

In the second embodiment of the invention a number of materials can beused in addition to paper. Clear plastic materials, such as Mylar, aswell as glass cloth of suitable thickness have been found to besatisfactory in most instances.

In general, the color producing reaction proceeds as follows: cellulosemolecules of the paper or the molecules of other reducing typepolysaccharides are split under the influence of the acid and heat toform monomeric reducing-type carbohydrates. The monomeric carbohydratesare then dehydrated and cyclicized to form cyclic aldehydes of the furantype such as furfural and hydroxymethyl furfural. Under the heat andacid conditions produced in the copy sheet, the aldehyde polymerizesforming characters which are dark black to brown in color depending uponthe particular formula that is used. As was pointed out above, thecarbohydrate that is applied to the base sheet in embodiment two of theinvention can be monosaccharide such as glucose, mannose, galactose,fructose, etc., a reducing disaccharide such as maltose, sucrose,lactose, and cellobiose, or polysaccharides such as starch andcellulose.

The sensitizing solution can also contain compounds which are able toinactivate the acids to a partial degree by complexing and/or partiallyneutralizing the acid. Compounds of this type would include urea,thiourea, triethanolamine, biuret, etc. These compounds tend tostabilize the formulation and prevent background discoloration. Furtherstabilization of the reproduction paper can be obtained by adding ametal sulfate to the composition in the manner described above.

Obviously many modifications and variations of the in vention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

We claim:

1. A process for graphically reproducing an original which comprises:placing an original having preferentially radiation absorbing areas incontact with a visibly heat-sensitive composition coated on a basesupport, said composition comprising a reducing carbohydrate selectedfrom the group consisting of glucose, mannose, galactose, maltose,lactose, fructose, arabinose, xylose, lyxose, ribose, cellobiose, andstarch and an organic acid, said acid having an ionization constantvarying from that of citric acid to that of meta-benzene disulfonicacid, and irradiating said original with heat producing radiations toincrease the temperature of the composition in the areas of saidsupported layer registering with said radiation absorbing areas to fromabout 240 F. to about 360 F., whereby said original is visiblyreproduced.

2. A process for graphically reproducing an original which comprises:placing an original having preferentially radiation absorbing areas incontact with a visibly heat-sensitive composition coated on a basesupport, said composition comprising a reducing carbohydrate, saidcarbohydrate being selected from the group consisting of glucose,mannose, galactose, maltose, lactose, fructose, arabinose, Xylose,lyxose, ribose, cellobiose, and starch, and an organic acid, said acidbeing selected from the group consisting of meta-benzene disulfonicacid, benzene sulfonic acid, p-toluene sulfonic acid, benzenetrisulfonic acid, citric acid, and sulfanilic acid, and irradiating saidoriginal With heat producing radiations to increase the temperature ofthe composition in the areas of said supported layer registering withsaid radiation absorbing areas to from about 240 F. to about 360 F.,whereby said original is visibly reproduced.

3. Reproduction material which comprises: a base support and a visiblyheat-sensitive coating on said support, said coating comprising amixture of a reducing carbohydrate selected from the group consisting ofglucose, mannose, galactose, maltose, lactose, fructose, arabinose,xylose, lyxose, ribose, cellobiose, and starch, and an organic acid,said acid having an ionization constant vary- 1g from that of citricacid to that of meta-benzene diulfonic acid. 4. Reproduction materialwhich comprises: a base upport and a visibly heat-sensitive coating onsaid supvort, said coating comprising a mixture of a reducing:arbohydrate selected from the group consisting of glucose, mannose,galactose, maltose, lactose, fructose, trabinose, xylosc, lyxose,ribose, cellobiose, and starch, 1nd an organic acid, said acid beingselected from the group consisting of meta-benzene disulfonic acid, ben-:ene sulfonic acid, p-toluene sulfonic acid, benzene triaulfonic acid,citric acid, and sulfanilic acid, and a stabilizing agent selected fromthe group consisting of urea, thiourea, biuret, and ethanolamine.

References Cited in the file of this patent UNITED STATES PATENTSBicknell et a1. Feb. 9, 1932 Martinez Jan. 23, 1934 Morrison 1 Jan. 13,1953 Miller et July 22, 1958 Owen Oct. 27, 1959 Sus et a1. Mar. 6, 1962

1. A PROCESS FOR GRAPHICALLY REPRODUCING AN ORIGINAL WHICH COMPRISES;PLACING AN ORIGINAL HAVING PREFERENTIALLY RADIATION ABSORBING AREAS INCONTACT WITH A VISIBLY HEAT-SENSITIVE COMPOSITION COATED ON A BASESUPPORT, SAID COMPOSITION COMPRISING A REDUCING CARBOHYDRATE SELECTEDFROM THE GROUP CONSISTING OF GLUCOSE, MANNOSE, GALACTOSE, MALTOSE,LACTOSE, FRUCTOSE, ARABINOSE, XYLOSE, LYXOSE, RIBOSE, CELLOBIOSE, ANDSTARCH AND AN ORGANIC ACID, SAID ACID HAVING AN IONIZATION CONSTANTVARYING FROM THAT OF CITRIC ACID TO THAT OF META-BENZENE DISULFONICACID, AND IRRADIATING SAID ORIGINAL WITH HEAT PRODUCING RADIATIONS TOINCREASE THE TEMPERATURE OF THE COMPOSITION IN THE AREAS OF SAIDSUPPORTED LAYER REGISTERING WITH SAID RADIATION ABSORBING AREAS TO FROMABOUT 240*F. TO ABOUT 360*F., WHEREBY SAID ORIGINAL IS VISIBLYREPRODUCED.